| *P. macrophthalmus Hall | |
| *P. monroensis Sarle | |
| *P. nasutus nov. | |
| *P. prolificus nov. |
VIII
SYSTEMATIC ACCOUNT OF THE EURYPTERIDA
Class arachnida
Subclass merostomata (Dana) Woodward
Order eurypterida Burmeister
Family eurypteridae Burmeister
Genus strabops Beecher 1901
Strabops thacheri Beecher
Strabops thacheri Beecher. American Journal of Science, n. s. 12:365, 1901
An eurypterid of extraordinary interest because of its age and completeness is a specimen obtained in the Cambric Potosi limestone of St François county, Missouri, which was studied by Prof. C. E. Beecher, and made by him the type of the genus and species: Strabops thacheri. Professor Beecher, evidently without his own knowledge had the use only of the relievo of this specimen and the counterpart has bsen found by the authors in the collections of Columbia University. The specimen is so preserved that the interior view of the dorsal side is shown in both cast and mold, and the latter is obviously the more distinct. Had it been at the disposal of the describer it would probably have prevented some evident misconceptions of structural details. The intaglio, cleaned with potash [pl. 4, fig. 5] and sharply cast [pl. 13, fig. 2], exhibits quite distinctly all true structure lines.
The specimen was correctly recognized by Dr Beecher as suggesting the genus Eurypterus. Its differences from the latter genus which, as such, constitute the generic characters were set forth by him as follows:
The cephalothorax is comparatively shorter and wider than in Eurypterus, the eyes are further forward, nearer together, and more oblique, and besides the telson but 11 abdominal somites can be determined on the dorsal side, instead of 12, as in Eurypterus. These differences are con-
